Method for producing fuel pellets and other lignocellulosic products with reduced hemicellulose, alkali metal and chlorine contents

ABSTRACT

At least one embodiment of the disclosure is directed to a method of producing a lignocellulose-based product with reduced contents of hemicellulose, chlorine, sulfur and alkali and alkaline earth metals. A biomass having up to 60% by weight of moisture prior to steam treatment is steam treated. A lignocellulose-based product with reduced contents of hemicelluloses, chlorine, sulfur and alkali and alkaline metals is produced.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application Ser. No. 61/762,615, filed Feb. 8, 2013, entitled “Fuel Pellets and Other Lignocellulosic Products with Low Alkali Metal and Chlorine Contents”, and U.S. Provisional Application Ser. No. 61/888,912, filed Oct. 9, 2013, entitled “Fuel Pellets and Other Lignocellulosic Products with Reduced Hemicellulose, Alkali Metal and Chlorine Contents” which are hereby expressly incorporated herein in their entirety.

BACKGROUND

Various embodiments disclosed herein are generally directed to a method of producing lignocellulosic fiber masses suitable, among other things for the manufacture of fuel pellets, in particular, from feedstocks that, because of high contents of substances, are regarded as deleterious to good combustion performance such as alkali metals and chlorides.

The high price of fossil fuels and the worldwide interest in replacing fossil fuels by others based upon renewable resources, has led to a dramatic increase in the demand for pelletized biomasses that can be burned in domestic stoves, and for products that can replace coal at power stations.

The most widely-used procedures involve compressing biomass in a pelletizing mill to make fuel pellets, which can be regarded as being a more compact energy source than the raw material itself. White pellets are made simply by compressing ground, dried biomass, meaning that coarser materials need to be subjected to an energy intensive size reduction step before pelletizing. The pellets typically contain about 10% moisture and need to be stored under cover, as they absorb water quickly and easily and lose their cohesiveness. They are also liable to create dust during transport and storage and thus risk causing a dust explosion.

So-called black pellets are made by subjecting dried biomass to medium pressure steam (steam explosion) or partial destructive distillation (torrefaction) before pelletizing.

Each of these methods produce a fuel pellet having the bulk of compounds of alkali metals, chlorine and sulfur present in the feed. Furthermore, their resistance to water is variable; white pellets must be stored under cover, while black pellets need to be stored under conditions that minimize leaching. Therefore, a need exists to produce a fuel pellet and other lignocellulosic products having reduced hemicellulose, alkali metal and chlorine contents. The present disclosure is directed toward a method of producing such a fuel pellet and/or other lignocellulosic product.

DETAILED DESCRIPTION

The methods described herein can be used to manufacture fuel pellets and other materials by steam treatment of biomass such as wood chips, bagasse, straw and energy crops that may be difficult to process without steam treatment and that may contain unacceptably high levels of compounds of alkali metals, chlorine and sulfur, for use as fuel pellets, with the additional possibility of avoiding an energy-demanding and often difficult drying step before steam treatment. These pellets can be stored under wet conditions for long periods of time with minimal loss of energy content and durability. They have higher energy contents and somewhat higher bulk densities than pellets made from the same feed by state-of-the-art methods and can be produced at lower temperatures, thus reducing the cost of plant needed to make them.

The use of steam treatment is necessary in order to convert the raw materials to a form that is more easily defibrillated and that can be efficiently dewatered mechanically, e.g., in a filter press before drying.

The steam treated materials made in accordance with the methods consist of two fractions: a water phase and a solid phase. The water phase will contain water soluble materials, primarily carbohydrates and minerals, primarily alkali metals and chlorides, plus some alkaline earth metals and sulfates. This product is eminently suitable, as a component in animal feed as a feedstock for fermentation or chemical processing.

The solid fraction can, as described above, be used to manufacture fuel pellets, but it can also be converted to fibrous materials for cartons and coarse paper or, with the addition of vegetable oil and, optionally, an acidic catalyst, as a component in wooden boards and mouldings.

One particularly advantageous application for the methods of this invention is the addition of an oil before or after steam treatment (or both) enabling the dried residue to be used as a thermoplastic compound. This is possible because the residue contains fewer substances such as reducing sugars that can react with and crosslink the lignin.

Lignocellulose-based products with low contents of hemicellulose, chlorine, sulfur, and alkali and alkaline earth metals are, in at least one embodiment, made by steam-treating an undried biomass, and washing the steam treated material to remove water soluble materials and, optionally, drying the residue.

In another embodiment, the lignocellulose-based products are made by steam treating a biomass, which may contain up to 60% by weight of moisture prior to steam treatment, defibrillating and washing the steam treated material to remove water soluble materials and, optionally, drying the residue.

In at least one embodiment, a vessel containing the biomass is evacuated before the introduction of steam, such that the total free oxygen content of the gas in the vessel into which the steam is injected is less than 10 volume % and preferably not more than 3 volume %.

In at least one embodiment, the lignocellulose-based products from biomass treated by injecting dry saturated or unsaturated steam at a temperature of at least 300° F. at a pressure of at least 52 psig and preferably between 120 and 280 psig into a reactor containing the biomass and maintaining the chosen pressure for between 1 and 30 minutes, the lower the steam pressure, the longer the residence time.

In at least one embodiment, the lignocellulose-based products from biomass treated by injecting dry saturated or unsaturated steam have a temperature of at least 150° C. at a pressure of at least 60 psig and between 120 and 240 psig into a reactor containing the biomass and maintaining the chosen pressure for between 3 and 30 minutes, the lower the steam pressure, the longer the residence time.

In another embodiment, up to 8% on biomass dry weight of an organic substance capable of functioning as a swelling agent or solvent for lignin during steam treatment and having a boiling point greater than 100° C. such as a fatty acid, a triglyceride, glycerol or a glycol is included in the biomass prior to the introduction of steam.

In another embodiment, up to 5% on biomass dry weight of an acidic catalyst such as nitric acid or acetic acid having a boiling point of less than 200° C. may be added after evacuation of the vessel and prior to the introduction of steam.

In another embodiment, hydrophobic lignocellulose-based products, including fuel pellets with low chlorine and alkali metal contents, made from steam processed materials as described herein are then water-washed, in at least one embodiment, in a counter-current process and the residue dried to less than 10% moisture by weight and in other embodiments, less than 5% moisture by weight, adding to it between 3% and 20% and between 5% and 8% by weight of an oil and then subjecting the whole to compression, for example, in a conventional molding or extrusion process.

In another embodiment, hydrophobic lignocellulose-based products, including fuel pellets with low chlorine, hemicellulose and alkali metal contents, made from steam processed materials as described herein are then subjected to dewatering and optionally water-washed, in at least one embodiment, in a counter-current process and the residue dried to less than 10% moisture by weight and in other embodiments, less than 5% moisture by weight, then adding sufficient of one of the above-mentioned lignin swelling agents or solvents to bring the total content of the said agent to at least 2% and preferably between 2 and 8% by weight and then subjecting the whole to compression, for example, in a conventional molding, pelletizing or extrusion process.

In another embodiment, the oil can be added to the dewatered filter cake prior to the final drying step, or immediately prior to the subsequent conversion process or to the biomass itself before steam treatment. In one embodiment, hydrophobic molded or extruded products, including fuel pellets, made as described herein, where the lignin swelling agent is an oil of vegetable origin that contains at least 20% by weight unsaturated fatty acid compounds, e.g., canola oil, palm oil, Jatropha oil, spent cooking oil, cottonseed oil, etc.

In another embodiment, the raw material is in the form of pellets, with or without the incorporation of at least 1% by weight of oil. This is particularly beneficial when processing materials of low bulk density, for example straw and bagasse.

In one embodiment, fuel pellets are made with the inclusion of up to 60 weight % of a brittle carbon source prior to pelletizing. The brittle carbon source being, for example, ground coal, petroleum coke, charcoal, or other thermally degraded biomass.

Thermoplastic molding and extrusion compounds made as described herein may contain at least 3% and not more than 25% by weight of an oil containing at least 20% unsaturates and having a boiling point of at least 150° C. at atmospheric pressure.

In order to further illustrate various embodiments of the present invention, the following examples are given. However, it is to be understood that the examples are for illustrative purposes only and are not to be construed as limiting the scope of the subject invention.

EXAMPLES Example 1 Fuel Pellets made without Brittle Additives in a Pellet Mill Raw Material:

100 parts by weight of chopped wheat straw or wheat straw pellets

0-5% by weight of an oil, preferably of vegetable origin, which can be contained in the pellets

Processing in the Reactor

The wheat straw or wheat straw pellets are transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 200° C. is introduced and the whole allowed to stand for 7 minutes once a pressure of 14.5 bar is reached and maintained.

Water Washing Procedure 1. 0-Stage Washing

The moisture content of the steam treated material is adjusted to at least 50% by weight and preferably between 60% and 70% by weight and compressed to remove as much moisture as possible, e.g. in a filter or screw press. The resulting solid material can be dried to the desired moisture content at once or the above process repeated as necessary before the final material is dried as required.

2. Multistage Washing

The steam treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase can be the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried as required.

Pellet Manufacture in a Pellet Mill

The filter cake, is dried to a moisture content of more than 2% and less than 15% by weight and, in one embodiment between 4% and 8% by weight either before or after the addition of oil, such that the total amount of oil contained in the filter cake immediately prior to it being converted to pellets is not less than 2% on dry matter and the whole pelletized in a mill such that the surface temperature of the pellets is ≧95° C. and preferably between 105° C. and 125° C.

These pellets have the following properties:

Bulk density: 800-820 kg/m³

Moisture content: <5%

Chlorine content (as chloride): <0.03%

K+Na content (as oxides): <0.2%

Water absorption after 24-hour immersion at 23° C.: Less than 3%

Leaching loss after 24-hour immersion in water at 23° C.: Less than 5%

Durability after 24-hour immersion in water: >90%

Energy content: ≧20 gJ/kg

HGI: 25-35

Example 2 Fuel Pellets made in an Extruder Raw Materials:

100 parts by weight of chopped wheat straw or wheat straw pellets

0-5% by weight of an oil, preferably of vegetable origin, which can be contained in the pellets

Processing in the Reactor

The wheat straw or wheat straw pellets are transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 200° C. is introduced and the whole allowed to stand for 7 minutes once a pressure of 14.5 bar is reached and maintained.

Water Washing Procedure 1. 0-Stage Washing

The moisture content of the steam treated material is adjusted to at least 50% by weight and preferably between 60% and 70% by weight and compressed to remove as much moisture as possible, e.g., in a filter or screw press. The resulting solid material can be dried to the desired moisture content at once or the above process repeated as necessary before the final material is dried as required.

2. Multistage Washing

The steam treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase can be the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried as required.

Pellet Manufacture

A sufficient quantity of oil is added to the filter cake, dried as per 1.1., to bring its total oil content to at least 4 weight % on dry matter and preferably between 5% and 8% by weight on dry matter. The mixture of oil and filter cake is processed in a pelletizing extruder such that the surface temperature of the pellets as they exit the die is not less than 90° C. and preferably between 105° C. and 125° C.

These pellets have the following properties:

Bulk density: 810-830 kg/m³

Moisture content: <3%

Chlorine content (as chloride): <0.03%

K+Na content (as oxides): <0.2%

Water absorption after 24-hour immersion at 23° C.: Less than 5%

Leaching loss after 24-hour immersion in water at 23° C.: Less than 3%

Durability after 24-hour immersion in water at 23° C.: >93%

Energy content: 22 gJ/kg

HGI: 25-35

Example 3 Fuel Pellets made with a Brittle Additive Raw Materials

100 parts by weight of chopped wheat straw or wheat straw pellets

0-5% by weight of an oil, preferably of vegetable origin, which can be contained in the pellets

Processing in the Reactor

The wheat straw or wheat straw pellets are transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 200° C. is introduced and the whole allowed to stand for 7 minutes once a pressure of 14.5 bar is reached and maintained.

Water Washing Procedure 1. 0-Stage Washing

The moisture content of the steam treated material is adjusted to at least 50% by weight and preferably between 60% and 70% by weight and compressed to remove as much moisture as possible, e.g., in a filter or screw press. The resulting solid material can be dried to the desired moisture content at once or the above process repeated as necessary before the final material is dried as required.

2. Multistage Washing

The steam treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase can be the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried as required.

Pellet Manufacture

At least 3 weight % on dry matter of an oil and at least 10% finely ground bituminous coal are added to the filter cake and the whole thoroughly mixed.

The whole is then transferred to a pellet mill and pelletized through a pellet die such that the surface temperature of the pellets as they exit the die is not less than 90° C. and preferably between 105° C. and 120° C.

These pellets have the following properties:

Bulk density: 810-820 kg/m³

Moisture content: <2%

Chlorine content (as chloride): <0.03%

K+Na content (as oxides): <0.2%

Water absorption after 24-hour immersion at 23° C.: Less than 8%

Leaching loss after 24-hour immersion in water at 23° C.: Less than 6%

Durability after 24-hour immersion in water at 23° C.: >90%

Energy content: 30 gJ/kg

HGI: 30-45

Example 4 The Use of Granulated Materials made in Accordance with the Methods as Disclosed herein as Thermoplastic Moulding and Extrusion Compounds

State-of-the-art steam-treated biomass used in the manufacture of so-called black pellets has the property of beginning to crosslink or thermosetting once subjected to the temperatures and pressures that typify pelletizing, whether in an extruder or a pellet mill. This is also the case when pellets containing vegetable oils are made from this type of biomass.

Most unexpectedly, this is not the case when materials made in accordance with this invention are processed and these materials have the exceptional property of being fully remeltable in the sense that they behave as thermoplastics rather than thermosets. This makes it possible to envisage their use as alternatives to conventional, fossil fuel based thermoplastics with all that this implies in terms of reducing petroleum consumption and the emission of greenhouse gases.

Unlike conventional thermoplastics, these products are also fully biologically degradable.

Raw Material:

100 parts by weight of fresh, birch-wood “microchips” (in at least one embodiment, the chips having at least 30% moisture content by weight).

Processing in the Reactor

The wood-chips are transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 210° C. is introduced and the whole allowed to stand for 5 minutes once a pressure of 18 bar is reached and maintained.

Water Washing Procedure 1. 0-Stage Washing

The moisture content of the steam treated material is adjusted to at least 50% by weight and preferably between 60 and 70% by weight and compressed to remove as much moisture as possible, e.g., in a filter or screw press. The resulting solid material can be dried to the desired moisture content at once or the above process repeated as necessary before the final material is dried as required.

2. Multistage Washing

The steam treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase can be the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried as required.

Granulate Manufacture

Up to 15 weight % on dry matter of Jatropha oil is added to the filter cake and the whole thoroughly mixed. This is conveyed to granulating extruder equipped with cooling, volatile venting and die and a cutting device and to produce a plastic granulate whose size is suitable for subsequent use in a(n injection) moulding machine or extruder. The material is processed such that its temperature in the extruder's mixing zone is maintained at least 120° C. and preferably between 140° C. and 160° C. and granulate made.

At least one embodiment of the method as disclosed can also be adapted to make a finished product such as a board, extruded profile or moulded part directly from the raw material itself, by processing it in an extruder having a die with the required profile or a suitably equipped injection moulding machine.

Example 5 Fuel Pellets made without Brittle Additives in a Pellet Mill Raw Material:

100 parts by weight of chopped miscanthus

Processing in the Reactor

The miscanthus is transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 200° C. is introduced and the whole allowed to stand for 7 minutes once a pressure of 14.5 bar is reached and maintained.

Water Washing Procedure

The steam-treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase is the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried to 5% moisture content by weight.

Pellet Manufacture

6 weight % on dry matter of Jatropha oil added to the filter cake and the whole thoroughly mixed. The mixture of oil and filter cake is pelletized in a mill through a die with a compression ratio of 6, so that the surface temperature of the pellets is 95° C. and preferably between 105° C. and 125° C.

These pellets have the following properties:

Bulk density: 800-820 kg/m³

Moisture content: <2%

Chlorine content (as chloride): <0.03%

K+Na content (as oxides): <0.2%

Water absorption after 24-hour immersion at 23° C.: Less than 3%

Leaching loss after 24-hour immersion in water at 23° C.: Less than 2%

Durability after 24-hour immersion in water: >98%

Energy content: 23 gJ/kg

HGI: 25-30

Example 6 Fuel Pellets made in an Extruder Raw Materials:

100 parts by weight of chopped miscanthus.

Processing in the Reactor

The miscanthus is transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 200° C. is introduced and the whole allowed to stand for 7 minutes once a pressure of 14.5 bar is reached and maintained.

Water Washing Procedure

The steam treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase is the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried to 5% moisture content.

Pellet Manufacture

9 weight % on dry matter of Jatropha oil added to the filter cake and the whole thoroughly mixed. The mixture of oil and filter cake is processed in a pelletizing extruder such that the surface temperature of the pellets is ≧95° C. and preferably between 105° C. and 125° C.

These pellets have the following properties:

Bulk density: 810-830 kg/m³

Moisture content: <1%

Chlorine content (as chloride): <0.03%

K+Na content (as oxides): <0.2%

Water absorption after 24-hour immersion at 23° C.: Less than 2%

Leaching loss after 24-hour immersion in water at 23° C.: Less than 3%

Durability after 24-hour immersion in water at 23° C.: >98%

Energy content: 24 gJ/kg

HGI: 25-30

Example 7 Fuel Pellets made with a Brittle Additive Raw Materials

100 parts by weight of chopped miscanthus.

Processing in the Reactor

The miscanthus is transferred to the reactor without drying. The whole is evacuated to −0.85 bar and allowed to stand for 2 minutes. Dry saturated steam having a temperature of 200° C. is introduced and the whole allowed to stand for 7 minutes once a pressure of 14.5 bar is reached and maintained.

Water Washing Procedure

The steam treated biomass is removed from the reactor vessel and transferred to a slurrying tank where the continuous phase is the final filtrate from the washing process. The whole is transferred to a counter-current washing system, e.g., a series of filter presses. The excess liquor from the first wash stage is removed for further treatment and the washing process continued counter-currently such that the residue in the final filtration step is washed with clean water. The final filter cake is removed and dried to 5% moisture content by weight.

Pellet Manufacture

9 weight % on dry matter of Jatropha oil and 30% by weight finely ground petroleum coke are added to the filter cake and the whole thoroughly mixed.

The whole is then transferred to a pellet mill and pelletized through a pellet die having a compression ratio of 5, making sure that the surface temperature of the pellets thus made is not less than 95° C. and preferably between 105° C. and 120° C.

These pellets have the following properties:

Bulk density: 830-850 kg/m³

Moisture content: <2%

Chlorine content (as chloride): <0.03%

K+Na content (as oxides): <0.2%

Water absorption after 24-hour immersion at 23° C.: Less than 4%

Leaching loss after 24-hour immersion in water at 23° C.: Less than 4%

Durability after 24-hour immersion in water at 23° C.: >96%

Energy content: 30 gJ/kg

HGI: 38-45

From the above description, it is clear that the present invention is well adapted to carry out the objects and to attain the advantages mentioned herein as well as those inherent in the invention. While presently preferred embodiments of the invention have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the invention disclosed. 

What is claimed:
 1. A method of producing pellets with reduced contents of hemicellulose, chlorine, sulfur and alkali and alkaline earth metals from a biomass material, comprising the steps of: providing a biomass having between 0% and 60% by weight of moisture into a reactor; and injecting steam at a temperature of at least 300° F. into the reactor containing the biomass material; maintaining a pressure for between 1 and 30 minutes; and forming the treated biomass material having reduced contents of hemicelluloses, chlorine, sulfur and alkali and alkaline metals into pellets.
 2. The method of claim 1 wherein the pressure is at least 52 psig.
 3. The method of claim 1 further comprising: adding up to 8% by weight of a swelling agent for lignin during steam treatment to the biomass material.
 4. The method of claim 3 wherein the swelling is added prior to injecting steam.
 5. The method of claim 3 wherein the swelling agent has a boiling point greater than 100° C.
 6. The method of claim 3 wherein the swelling agent is a fatty acid, a triglyceride, glycerol or a glycol.
 7. The method of claim 1 further comprising: evacuating the reactor before injecting the steam.
 8. The method of claim 7 wherein the reactor is evacuated such that the total free oxygen content of gas in the reactor is between 3% and 10% by volume.
 9. The method of claim 1 further comprising: adding between 0% and 5% by weight of an acid catalyst to the biomass material.
 10. The method of claim 8 wherein the acid catalyst has a boiling point of less than 200° C.
 11. The method of claim 8 wherein the acid catalyst is added prior to injecting the steam.
 12. The method of claim 1 further comprising: washing the pellets formed from the treated material.
 13. The method of claim 12 further comprising: drying the washed pellets to less than 10% moisture by weight.
 14. The method of claim 13 further comprising: adding between 3% and 20% by weight of an oil.
 15. The method of claim 14 further comprising: compressing the treated material in a molding or extrusion process.
 16. The method of claim 12 further comprising: adding between 3% and 20% by weight of an oil.
 17. The method of claim 16 wherein the oil contains at least 20% by weight unsaturated fatty acid compounds.
 18. The method of claim 1 further comprising: adding between 0% and 60% by weight of a brittle carbon source.
 19. The method of claim 18 wherein the brittle carbon source is thermally degraded biomass.
 20. The method of claim 1 wherein the surface temperature of the pellets is greater than 95° C. 